1. Field of the Invention
The present invention relates to an electron beam writing method and a fine pattern writing system for writing a fine pattern according to a desired uneven pattern when manufacturing an imprint mold, magnetic transfer master substrate, or the like for a high density magnetic recording medium, such as a discrete track medium, bit pattern medium, or the like.
The invention also relates to a method for manufacturing an uneven pattern carrying substrate, including an imprint mold, magnetic transfer master substrate or the like, having an uneven pattern surface formed through a writing step performed by the electron beam writing method described above. The invention further relates to a method for manufacturing a magnetic disk medium having an uneven pattern transferred thereto from the uneven pattern carrying substrate or imprint mold, and a method for manufacturing a magnetic disk medium having a magnetic pattern transferred thereto from the magnetic transfer master substrate.
2. Description of the Related Art
A magnetic disk medium is provided with a fine pattern corresponding to servo signal, address signal, and the like by an uneven pattern, a magnetic pattern, or the like. As for the method for forming such fine patterns, an electron beam writing method in which a pattern is written on a substrate applied with a resist by irradiating an electron beam thereon while rotating the substrate is proposed as described, for example, in U.S. Pat. No. 7,026,098 and Japanese Unexamined Patent Publication No. 2003-248981.
The electron beam writing method described in U.S. Pat. No. 7,026,098 is a method in which when, for example, writing a rectangular or parallelogram element constituting a servo pattern extending in a track width direction, the electron beam is deflected in a radial direction while being vibrated rapidly in a circumferential direction, thereby scanning the beam so as to completely fill the area of the element.
The electron beam writing method described in Japanese Unexamined Patent Publication No. 2003-248981 is a method in which when, for example, writing elements of a recording bit string with a constant length in a track width direction and different lengths in a track direction, the electron beam is rapidly vibrated in a radial direction with the amplitude thereof being adjusted as the substrate is rotated.
Further, as on/off writing method, a method in which pattern writing is performed by on/off irradiating an electron beam on a substrate applied with a resist according to the shape of a pattern while rotating the substrate, and shifting the substrate or electron beam irradiation unit by one beam width every rotation of the substrate in a radial direction is also known.
FIG. 6 shows an example fine pattern to be recorded on a magnetic disk medium, such as a hard disk. The concentric tracks in an annular region of disk-shaped disk 1 excluding outer circumferential portion 1a and inner circumferential portion 1b are made up of a plurality of sectors, each including preformatted area 2 and data area 5. Preformatted area 2 includes, for example, preamble, address signal, burst signal, and the like recorded typically by a magnetic pattern (fine pattern) or the like. Preformatted areas 2 are formed in elongated areas extending substantially radially in each sector from the center at regular intervals with respect to concentric tracks of disk 1. Note that preformatted areas 2 in this example are formed in curved radial continued in radial directions.
A portion of preformatted area 2 recorded on disk 1 includes address information recorded by a fine pattern (magnetic pattern) like that shown, as an example, in FIG. 7. The address information is formed of a fine pattern that includes short rectangular elements 3 and long rectangular elements 4 disposed on concentric tracks T1 to T4 in a mixed fashion.
As illustrated in FIG. 8A in an enlarged form, short element 3 in preformatted area 2 (magnetic pattern) recorded on a magnetic disk medium corresponds to 1-bit signal length “T”, and long element 4 has a track direction length corresponding to 2-bit signal length “2T”.
FIG. 8B illustrates fine pattern 12 to be written on substrate 10 of the present invention, to be described later, by an electron beam when, for example, producing a master substrate for performing magnetic transfer recording on the magnetic disk medium described above. Writing lengths of short element 13 and long element 14 formed on the master substrate for magnetically transferring short element 3 and long element 4 to the magnetic disk medium are reduced by a predetermined ratio with respect to 1-bit signal length “T” and 2-bit signal length “2T” on the disk medium respectively, resulting in “kT” for short element 13 and “2kT” for long element 14. This is influenced by magnetization characteristic at the time of magnetic transfer (transfer bleeding) and size variation at the time of etching, and reduction ratio k varies depending on various conditions.
For a 2-bit signal, long writing element 14 of the present invention is written as an integrated rectangular element having a length of 2kT centered on the middle position of 2-bit signal length 2T.
That is, the following have been found out. When long element 14 is formed by writing short elements 13 in adjacent 1-bit signal areas, an unwritten gap (T-kT) will present between adjacent elements 13. Then, if a magnetic transfer master substrate is produced with this element and magnetic transfer is performed on a magnetic disk medium using the master substrate, an area having a different magnetic pole according to the gap will present in the middle portion of long element 4 shown in FIG. 8A in a magnetic pattern formed on the magnetic disk medium after the magnetic transfer, which poses a problem of address information readout error. In order to record long element 4 with 2-bit length 2T on a magnetic disk medium as an integrated signal, it is necessary to write long element 14 as one element with reduced writing length 2kT like that shown in FIG. 8B.
The fine pattern representing an address signal shown in FIG. 7 is an example of address information in a hard disk pattern after Manchester conversion. The Manchester conversion converts binary numbers “0” and “1” to “01” and “10” respectively, thus having always “1”. Whereas, in dibit conversion, binary numbers “0” and “1” are converted to “00” and “01” respectively. That is, “1” does not appear in the second digit, and instead “0” appears more.
When address information in a hard disk pattern is converted by the dibit conversion and formed in an uneven pattern on a magnetic transfer master substrate, flat portions corresponding to “0” appears more than convex portions corresponding to “1” because “0” appears more. Consequently, if magnetic transfer is performing by bringing the master substrate and a magnetic disk medium into close contact with each other and applying a transfer magnetic field, flat portions other than convex portions of the master substrate, which normally do not brought into close contact with the magnetic disk medium, are brought into close contact with the surface of the medium, causing a problem that an erroneous signal is magnetically transferred to the disk medium. In view of this, it is proposed that information including address information be converted by Manchester conversion, which causes more convex portions to appear in an uneven pattern on a master substrate, for pre-formatting a magnetic disk medium by magnetic transfer.
In a signal train converted by Manchester conversion, a binary number “01” is converted to “0110”, resulting in that “1” corresponding to a convex portion of a fine pattern appears in succession. Thus, when writing such a portion in the fine pattern, the adjacent short elements must be written as one long element as described above.
In the mean time, exposure bleeding occurs in electron beam exposure writing on a resist in which a portion wider than the portion actually scanned by the electron beam reacts and is exposed. Therefore, it is also necessary to reduce the exposure width scanned by the electron beam shorter than the actual signal length on the magnetic disk medium.
The electron beam writing methods disclosed in U.S. Pat. No. 7,026,098 and Japanese Unexamined Patent Publication No. 2003-248981 do not mention about a method for writing a long element like that described above, and there is a demand for a method capable of writing such a long element on a predetermined position accurately and rapidly.
In particular, writing of a fine pattern having short elements and long elements in a mixed fashion as described above has a problem that a long element representing “11”, which should be written integrally, is written separately, having a gap in the middle, thereby causing faulty transfer or erroneous signal.
In view of the circumstances described above, it is an object of the present invention to provide an electron beam writing method capable of writing a reduced element having a predetermined exposure width in a track direction without a gap in the middle thereof for a fine pattern having short elements and long elements in a mixed fashion.
It is a further object of the present invention to provide a method for manufacturing an uneven pattern carrying substrate, such as an imprint mold or a magnetic transfer master substrate, having a fine pattern accurately written by an electron beam, and a method for manufacturing a magnetic disk medium using the uneven pattern carrying substrate in which an uneven pattern or a magnetic pattern is transferred from the uneven pattern carrying substrate to the magnetic disk medium.